1. Field of the Invention
The invention relates to a multi-stand roll train for the longitudinal rolling of seamless steel tubes in a continuous rolling process around an internal die, using integrated two-high stands staggered by 90.degree. with correspondingly grooved rollers, which are radially adjustable relative to one another.
2. Description of the Prior Art
A roll train of this type is known from DE-As 10 17 122. Longitudinal rolling processes having an internal die and a plurality of stands arranged one behind the other as a continuous train have long been known. There have been consistent efforts to reduce the number of roll stands in the continuous train, because a relatively large number of stands represents a considerable investment expense. Over the past two decades it has proved possible to reduce the number of stands from eight to five. Furthermore, suggestions have been made to reduce the number of stands to four or even three.
In all cases, however, it is necessary for the final two stands in the direction of rolling to have a round groove, so that a constant wall thickness can be obtained around the perimeter of the tube. Because differences in the wall thickness around the perimeter would arise if the round groove were adjusted, the prior art produces different wall thicknesses by using mandrels of different diameters.
Using a given mandrel diameter, the desired wall thickness is attained through the radial adjustment of the rollers. However, if the rollers are run together, the thinnest wall will always be rolled at the bottom of the groove, while the wall will remain thicker in the area of the groove sides. Because the two-high stands are staggered by 90.degree., the result is four thinner and thicker wall areas, each 90.degree. from the next, distributed around the perimeter of the tube.